1. Field of the Invention
The invention relates to a technology for detecting an abnormality of an oil level sensor that detects the oil level in the oil pan of an internal combustion engine.
2. Description of the Related Art
For example, Japanese Patent Application Publication No. 3-130519 (JP-A-3-130519, Page 5, FIG. 3, FIG. 5) and Japanese Patent Application No. 5-163923 (JP-A-5-163923, Page 3 to 4, FIG. 5) each recite a technology for detecting abnormalities of upper and lower oil level detectors (upper and lower switches) of an oil level sensor that are provided in the oil pan of an internal combustion engine.
In the technologies described in the above publications, based on the premise that a specific combination of the outputs of the two oil level detectors does not last a long time because the oil surface is ruffled as the vehicle runs, it is determined that the oil level detector or portions have an abnormality when a specific combination of the outputs of the two oil level detectors lasts a long time.
With the increasing importance of exhaust purification, devices for purifying exhaust gas, such as catalysts and filters, have been increasingly used. In some internal combustion engines incorporating such an exhaust purification device, fuel is supplied to the exhaust purification device from the combustion chamber side in order to burn and thus remove the particulate matter (PM) accumulated in the exhaust purification device or to promote or continue the catalyst reactions. For example, in some diesel engines, so-called after-injection or post-injections are performed.
When such fuel injection for supplying fuel to an exhaust purification device is performed in each combustion chamber, fuel tends to be mixed into the engine oil through between the cylinder wall and the piston. The more the fuel is mixed into the engine oil, the viscosity of the engine oil decreases, which may result in stuck up due to heat or excessive rising of the oil level in the oil pan, causing a leak of the engine oil (e.g., a leak of the engine oil to the PCV (Positive Crankcase Ventilation) path via which blow-by gas is supplied to each combustion chamber).
As such, in order to promptly detect that fuel has been mixed into the engine oil, an oil level detector is provided at a position higher than the level at which the oil surface normally remains when the internal combustion engine is operating, and if the oil level continues to be above the position of the oil level detector during the operation of the internal combustion engine, it is determined that fuel has already been mixed into the engine oil and thus the engine oil needs to be changed.
However, in a case where the oil level detector is out of order continuing to output a signal indicating that the oil level is lower than the position of the oil level detector, the mixing-in of fuel can not be detected, and therefore problems, such as a decrease in the oil viscosity and excessive rising of the oil level, may occur.
To counter this, one option is to determine that the oil level detector has an abnormality when the oil level detector has continued to produce a specific output for a long time, based on the premise that it is impossible for the oil level detector to continue to produce a specific output for a long time if it is in the normal condition, as in the methods employed in the above-stated publications.
This abnormality detection method, however, takes a long time before detecting an abnormality with precision. If an abnormality can not be detected and no counter-measure for the abnormality is taken for a long time, it allows fuel to be mixed into the engine oil.